Method and apparatus for preheating and feeding material

ABSTRACT

A casting furnace for preheating and melting solid feed material includes a melting chamber with a melting hearth therein and a feed chamber in fluid communication with the melting chamber for conveying the solid material into the melting chamber. A heat source melts the feed material within the melting hearth and produces surplus heat used to preheat the solid feed material. Preferably, gas is heated by the heat source and moved into the feed chamber to preheat the feed material while it is conveyed toward the melting hearth. The heated gas is recycled back into the melting chamber to be re-heated therein and reused to preheat additional feed material in the feed chamber. Where the heat source in the melting chamber includes a plasma torch, the gas is recycled via the plasma torch, which ionizes the gas to create a plasma plume for melting the solid material.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates generally to a furnace for melting metals andother materials in which a solid feed material is preheated. Moreparticularly, the invention relates to such a furnace wherein the solidfeed material is preheated by heated gas from within the meltingchamber. Specifically, the invention relates to such a furnace in whicha plasma torch used for melting the material produces the heated gas andwherein the gas is cooled and recycled for re-use by the plasma torch.

2. Background Information

Furnaces for melting metal and other materials typically have a meltingchamber with a melting hearth disposed therein in which the metal orother material is melted. Various types of heat sources provide the heatin order to melt the material within the melting hearth. It would behelpful to preheat the solid feed material which is fed into the meltinghearth in order to reduce the total melting time, thereby increasingproductivity. An increased melt rate can also increase the depth andsize of the molten pool, the super heat of the molten material, liquidmetal mixing and the capability for chemistry control. The increasedmelt rate would also increase the probability of removing defects suchas high density inclusions (HDIs) and improve the surface quality incontinuously casting ingots or slabs. The present invention providessuch preheating and the above-listed benefits.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method comprising the steps ofpreheating solid feed material; moving the heated solid feed materialinto a melting hearth disposed within a melting chamber; and melting thesolid material in the melting hearth.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a sectional view taken from the side of the furnace showingthe preheating system of the present invention.

FIG. 2 is similar to FIG. 1 and shows an alternate feeding mechanism.

Similar numbers refer to similar parts throughout the specification.

DETAILED DESCRIPTION OF THE INVENTION

The furnace and preheating system of the present invention is indicatedgenerally at 10 in FIG. 1; and a second embodiment is indicatedgenerally at 100 in FIG. 2. While furnace 10 is configured as a plasmaarc melting furnace, various concepts of the invention are applicable toother types of furnaces as well. Furnace 10 includes an insulatedmelting chamber 12 with a withdrawal chamber 14 disposed therebelow andin fluid communication therewith, and an insulated feed chamber 16 whichis disposed beside melting chamber 12 and in fluid communicationtherewith. A melting hearth 18 which defines a melting cavity 20 and acontinuous casting mold 22 are disposed within melting chamber 12. Alift 24 is disposed below mold 22, is partially within withdrawalchamber 14 and is movable up and down as shown by Arrow A into and outof melting chamber 12. First and second heat sources which arepreferably in the form of first and second plasma torches-26 and 28extend from above melting chamber 12 through an upper wall thereof andinto chamber 12 for respectively providing heat above mold 22 andmelting hearth 18. More particularly, second torch 28 provides heat tomelt pieces 30 of solid feed material which are moved into meltingcavity 20 as indicated at Arrow B to form molten material 32 withincavity 20 which is subsequently poured or otherwise moved as indicatedat Arrow C into mold 22 to produce a molded body in the form of an ingot33 as lift 24 is lowered. First torch 26 provides heat to moltenmaterial 32 within mold 22 in order to control the solidification ratesand so forth. While pieces 30 of feed material are typically metal,other materials are contemplated as well. Furnace 10 is suitable formelting titanium alloys or superalloys.

With continued reference to FIG. 1, feed chamber 16 has a first end 34adjacent which it is connected to melting chamber 12 and a secondopposed end 36 distal melting chamber 12. Feed chamber 16 defines anentrance opening 38 adjacent second end 36 for receiving pieces 30 ofsolid feed material from outside feed chamber 16. Furnace 10 includes afeed assembly 40 comprising an input mechanism in the form of anactuator 42 which is disposed external to feed chamber 16 and includes apiston 44 which is moveable back and forth as indicated by Arrow D. Feedassembly 40 also includes a conveyor assembly 46 disposed within feedchamber 16 and extending partially into melting chamber 12. Conveyingassembly 46 includes a conveyor belt 48 which is revolvingly mounted ona pair of rotatable members 50A and 50B disposed at respective opposedends of conveying assembly 46. Input mechanism 42 includes asubstantially horizontal platform 45 which is aligned with asubstantially horizontal upper portion 52 of conveyor belt 48. Feedchamber 16 includes a heating passage 54 through which pieces 30 ofsolid feed material are moved as indicated by Arrows E from entranceopening 38 to melting hearth 18. More particularly, piston 44 ofactuator 42 is operated to move pieces 30 of solid feed material from atop platform 45 onto upper portion 52 of conveyor belt 48 wherebyoperation of conveying assembly 46 moves pieces 30 as indicated atArrows E along upper portion 52 to feed pieces 30 into melting cavity 20of hearth 18.

With continued reference to FIG. 1 and in accordance with a feature ofthe invention, melting chamber 12 and feed chamber 16 are part of arecirculation pathway 56 which includes various conduits or ducts 58, aheat exchanger 60, a scrubber 62 for removing impurities from gas and apump 64, all of which are in fluid communication with one another.Recirculation pathway 56 is configured to recirculate a gas 66therethrough so that gas 66 is heated within melting chamber 12 andmoved into feed chamber 16 in order to heat pieces 30 of solid feedmaterial prior to entering melting cavity 20 to be melted by torch 28.Gas 66 is typically an inert gas and when used with plasma torches suchas torch 28 is typically helium or argon or a mixture thereof.

With reference to FIG. 1, the operation of furnace 10 is furtherdetailed. Pump 64 is operated to pump gas 66 through a segment of duct58 as indicated at Arrows F into second torch 28. Gas 66 is then movedas indicated at Arrows G through torch 28, which heats and ionizes gas66 to generate a plasma plume 68 for heating and melting pieces 30 andmaintaining molten material 32 in melting hearth 18. Where other plasmatorches such as torch 26 are used, gas 66 may also be circulated throughsuch other plasma torches as indicated at Arrow G2. The core of plasmaplume 68 typically has a temperature on the order of about 10,00° C. andgas 66 within chamber 12 has a temperature typically on the order ofabout 1,000° C. Thus, gas 66 becomes a heated gas within chamber 12which moves as indicated by Arrows H into and through heating passage 54of feed chamber 16 from first end 34 thereof to second end 36 thereof.

As the heated gas 66 is moved as indicated by Arrows H away from meltingchamber 12, pieces 30 of solid feed material are moved toward meltingchamber 12 in substantially the opposite direction. Due to the elongatednature of chamber 16, the invention thus takes advantage of a relativelylengthy heating passage 54 in order to allow substantial time for theheat exchange between heated gas 66 and pieces 30. The heated gas 66will of course be substantially hotter adjacent first end 34 thanadjacent second end 36 of feed chamber 16. The insulated walls ofmelting chamber 12 and feed chamber 16 help maintain heated gas 66 ashot as is feasible in order to better take advantage of the heatexchange between gas 66 and pieces 30.

Heated gas 66 reaches second end 36 of feed chambers 16 and exitsthrough a vent or segment of duct 58 as indicated at Arrow J into heatexchanger 60 and then through another segment of duct 58 as indicated atArrow K into scrubber 62 and finally through another segment of duct 58as indicated at Arrow L back to pump 64 whereby gas 66 has beencompletely recirculated. Heat exchanger 60 cools gas 66 down to atemperature which is suitable for scrubbing of gas 66 via scrubber 62,typically at about room temperature.

With reference to FIG. 2, furnace 100 is described. Furnace 100 issimilar to furnace 10 except that furnace 100 includes a feed assembly102 which differs from feed assembly 40 of furnace 10 in that assembly102 includes a conveying assembly 104 which is different than that offurnace 10. More particularly, conveying assembly 104 is a walking tablesuitable for receiving pieces 30 from platform 45 and delivering pieces30 as shown by Arrows E into melting cavity 20 of hearth 18. Otherwise,the operation of furnace 100 is the same as furnace 10.

Thus, furnaces 10 and 100 provide systems that are configured to preheatsolid feed material prior to placing the feed material in the meltinghearth where it is melted. While the invention contemplates preheatingsolid feed material by any mechanism, it also advantageously utilizesthe surplus heat produced by the primary heat sources which are used formelting the feed material within the melting hearth and melting chamber.It is contemplated that this surplus heat produced by the primary heatsource within the melting chamber may be transferred to preheat thesolid feed material by means of radiation, convection, conduction or anycombination of these. However, the movement of the heated gas is apreferred mode of accomplishing this transfer of heat in a moreefficient manner. While the exemplary embodiment preferably utilizes atleast one plasma torch whereby the heated gas is recirculated for reuseby the plasma torch, it is also contemplated that gas which is heated bythe surplus heat within a melting chamber may be transferred in othermanners in order to preheat solid feed material. For example, infurnaces which are under a vacuum to eliminate or substantiallyeliminate gasses within the melting chamber, conduits may be configuredto pass through a portion of the melting chamber so that gas passingthrough such conduits is heated within the melting chamber by thesurplus heat and then transferred to a separate feed chamber or the likein order to preheat the solid feed material. Other variations which arewithin the scope of the present invention will be evident to one skilledin the art.

In the foregoing description, certain terms have been used for brevity,clearness, and understanding. No unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art because suchterms are used for descriptive purposes and are intended to be broadlyconstrued.

Moreover, the description and illustration of the invention is anexample and the invention is not limited to the exact details shown ordescribed.

1. A method comprising the steps of: preheating solid feed material bymoving the solid feed material within a melting chamber in a firstdirection and moving heated gas within the melting chamber along thefeed material in a second direction generally opposite the firstdirection; moving the heated solid feed material into a melting cavityof a melting hearth disposed within the melting chamber; and melting thesolid material in the melting cavity of the melting hearth. 2-20.(canceled)
 21. The method of claim 1 further comprising the step offeeding solid feed material into the melting chamber through a feedentry port formed in a sidewall bounding the melting chamber; andwherein the step of preheating comprises the step of preheating solidfeed material by moving the solid feed material in the first directionfrom the feed entry port toward the melting hearth and moving the heatedgas in the second direction from adjacent the melting hearth to adjacentthe feed entry port.
 22. The method of claim 21 wherein the step ofpreheating comprises the step of preheating solid feed material bymoving the solid feed material in the first direction from the feedentry port to the melting hearth atop a conveyor assembly disposed inthe melting chamber and having a first end adjacent the feed entry portand a second opposed end adjacent the melting hearth.
 23. The method ofclaim 22 wherein the step of preheating comprises the step of preheatingsolid feed material by moving the solid feed material atop an uppersurface of the conveyor assembly onto an upper surface of the meltinghearth adjacent the melting cavity and the upper surface of the conveyorassembly.
 24. The method of claim 23 wherein the step of moving theheated solid feed material comprises the step of sliding the heatedsolid feed material along the upper surface of the melting hearth tomove it into the melting hearth.
 25. The method of claim 22 wherein thestep of moving the solid feed material in the first direction comprisesthe step of moving the solid feed material in the first direction fromthe feed entry port to the melting hearth atop one of a conveyor beltassembly and a walking table disposed in the melting chamber.
 26. Themethod of claim 22 further comprising the step of pushing solid feedmaterial through the feed entry port onto the first end of the conveyorassembly.
 27. The method of claim 26 wherein the step of pushingcomprises the step of pushing solid feed material through the feed entryport on a platform extending from outside the chamber into the entryport and adjacent the first end of the conveyor assembly.
 28. The methodof claim 21 wherein the step of moving the heated gas comprises the stepof moving the heated gas in the second direction from adjacent themelting hearth to a gas exit port formed in the sidewall adjacent thefeed entry port; and further comprising the step of moving the gas outof the melting chamber through the gas exit port.
 29. The method ofclaim 28 further comprising the step of recycling the gas which exitedthrough the gas exit port back into the melting chamber adjacent themelting hearth and distal the feed entry port.
 30. The method of claim29 wherein the step of melting comprises the step of melting the feedmaterial in the melting hearth with a first plasma torch positionedabove the melting hearth distal the feed entry port; and wherein thestep of recycling comprises the step of recycling the gas back into themelting chamber through the plasma torch.
 31. The method of claim 28further comprising the steps of pouring molten material from the meltinghearth into a mold disposed in the melting chamber distal the feed entryport; and recycling the gas which exited through the gas exit port backinto the melting chamber adjacent the mold.
 32. The method of claim 31further comprising the step of heating material in the mold with aplasma torch positioned above the mold distal the feed entry port; andwherein the step of recycling comprises the step of recycling the gasback into the melting chamber through the plasma torch.
 33. The methodof claim 1 wherein the step of moving the heated solid feed materialcomprises the step of sliding the heated solid feed material along anupper surface of the melting hearth adjacent the melting cavity to moveit into the melting hearth.
 34. The method of claim 33 wherein the stepof preheating comprises the step of preheating solid feed material bymoving the solid feed material with a conveyor assembly disposed in themelting chamber on an upper surface of the conveyor assembly which isadjacent the upper surface of the melting hearth; and further comprisingthe step of transferring the preheated solid feed material from theupper surface of the conveyor assembly onto the upper surface of themelting hearth.
 35. The method of claim 34 wherein the step oftransferring comprises the step of contacting both upper surfacessimultaneously with a piece of the preheated solid feed material. 36.The method of claim 1 further comprising the step of pouring moltenmaterial from the melting hearth into a mold disposed in the meltingchamber.
 37. The method of claim 36 further comprising the step ofpouring molten material from the melting hearth into a continuouscasting mold disposed in the melting chamber.
 38. The method of claim 36further comprising the steps of forming a molded body with the mold; andremoving the molded body from the melting chamber.
 39. The method ofclaim 38 wherein the step of removing comprises the step of lowering themolded body from the melting chamber on a lift.
 40. The method of claim36 further comprising the steps of heating material in the mold with aplasma torch positioned above the mold; heating gas within the meltingchamber with the plasma torch to produce heated gas used in the step ofpreheating.
 41. The method of claim 40 further comprising the steps ofrecycling the gas back into the melting chamber via the plasma torch;and generating a plasma plume with the gas.
 42. The method of claim 1wherein the step of melting comprises the step of melting the feedmaterial in the melting cavity with a first plasma torch positionedabove the melting hearth; and further comprising the steps of pouringmolten material from the melting hearth into a mold disposed in themelting chamber; heating material in the mold with a second plasma torchpositioned above the mold; heating gas within the melting chamber withthe first and second plasma torches to produce heated gas used in thestep of preheating.
 43. The method of claim 42 further comprising thesteps of recycling the gas back into the melting chamber via the firstand second plasma torches; and generating a plasma plume in each torchwith the gas.
 44. A method comprising the steps of: preheating solidfeed material by moving the solid feed material within a melting chamberfrom a feed entry port formed in a sidewall bounding the melting chambertoward a melting hearth disposed in the melting chamber and movingheated gas from adjacent the melting hearth out of the melting chamberthrough a gas exit port formed in the sidewall adjacent the feed entryport; moving the preheated solid feed material into the melting hearth;and melting the preheated solid feed material in the melting hearth. 45.The method of claim 44 wherein the step of preheating comprises the stepof preheating by moving the solid feed material on a conveyor assemblyin the melting chamber having a first end adjacent the feed entry portand a second opposed end adjacent the melting hearth and moving heatedgas from the second end to the first end.
 46. The method of claim 44further comprising the step of pouring molten material from the meltinghearth into a mold disposed in the melting chamber; and wherein the stepof moving heated gas comprises the step of moving heated gas fromadjacent the mold out of the melting chamber through the gas exit port.47. A method comprising the steps of: preheating solid feed materialwithin a melting chamber in which a melting hearth is disposed; slidingthe preheated solid feed material along an upper surface of the meltinghearth adjacent a melting cavity thereof to move it into the meltingcavity; and melting the preheated solid feed material in the meltingcavity.
 48. The method of claim 47 wherein the step of preheatingcomprises the step of preheating solid feed material by moving the solidfeed material with a conveyor assembly disposed in the melting chamberon an upper surface of the conveyor assembly which is adjacent the uppersurface of the melting hearth; and further comprising the step oftransferring the preheated solid feed material from the upper surface ofthe conveyor assembly onto the upper surface of the melting hearth. 49.The method of claim 48 wherein the step of transferring comprises thestep of contacting both upper surfaces simultaneously with a piece ofthe preheated solid feed material.